Organic photoconductor for electrophotography

ABSTRACT

Photoconductive materials are prepared from an N-aryl carbazole compound and a Lewis acid. The materials are charge transfer complexes with the N-aryl carbazole such as N-phenylcarbazole acting as an electron donor and the Lewis acid such as 2, 4, 7trinitro-9-fluorenone acting as an electron acceptor. The molar ratio of the donor to the acceptor can be in the range from 1:0.5 to 1:1.

United States Patent [191 Montillier 1 1 Mar. 18, 1975 1 ORGANICPHOTOCONDUCTOR FOR ELECTROPHOTOGRAPHY [75] Inventor: Jean-PierreMontillier, Manchester.

Conn.

[52] US. Cl. 96/1.5 [51] Int. Cl. G03g 5/06, (303g 7/00 [58] Field 01Search 96/15; 260/315 [56] References Cited UNITED STATES PATENTS3.287.119 11/1966 Hoegl 1. 260/315 3.408.189 10/1968 Mammine 96/].53511.966 5/1970 Shattuck et a1 96/15 3,579.33] 5/1971 Mee et a1 96/153.615.412 10/1971 Hassel 90/15 3.655.378 4/1972 Contors et a1. 3.765.88310/1973 Endo et a]. Jo/1.5

Primary Examiner-Norman G. Torchin Assistant Examiner-J. P. BrammerAttorney, Agent, or FirmWilliam D. Soltow, Jr.; Albert W. Scribner;Peter Vrahotes [57] ABSTRACT Photoconductive materials are prepared froman N- aryl carbazole compound and a Lewis acid. The materials are chargetransfer complexes with the N-aryl carbazole such as N-phenylcarbazoleacting as an electron donor and the Lewis acid such as 2. 4. 7-trini'tro-9-fluorenone acting as an electron acceptor. The molar ratio of thedonor to the acceptor can be in the range from 1:0.5 to 1:1.

3 Claims, No Drawings ORGANIC PHOTOCONDUCTOR FOR ELECTROPHOTOGRAPHYBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an organic photoconductive composition comprising N-arylcarbazole and more particularly to the use of N-aryl carbazole incombination with a nitrofluorenone and their use in electrophotographicprocesses.

2. Description the Prior Art The forming and developing of images on thesurfaces of certain photoconductive materials by electrostatic means isnow well known. Carlson, in U.S. Pat. No. 2,297,691 teaches the basicxerographic process, which involves uniformly charging a photoconductiveinsulating layer and then exposing the layer to a lightand-shadow imagewhich dissipates the charge on the portions of the layer which areexposed to light. The electrostatic latent image formed on the layercorresponds to the configuration ofthe light-and-shadow image. Inanother modification, a latent electrostatic image is formed on thephotoconductive insulating layer by charging the layer in imageconfiguration. A finely divided developing material comprising acolorant called a toner and a toner carrier is deposited on the imagelayer. The developing material is normally attracted to those portionsof the layer which retain a charge, thereby forming a powder imagecorresponding to the latent electrostatic image. The powder image maythen be transferred to paper or any other receiving surface. The powderimage is permanently bonded to the paper by any suitable fixing means.Typically, a heating process, called fusing, is used, as described inU.S. patents such as U.S. Pat. Nos. as 2,357,809, 2,89l,Ull and3,079,342.

It is possible to employ a wide variety of photoconductive insulatingmaterials in the electrostatic process. For example, Carlson. in U.S.Pat. No. 2,297,691 discloses photoconductive insulating materials suchas anthracene, sulfur, selenium or mixtures thereof.

These materials generally have sensitivity in the blue or nearultraviolet range, and all but selenium have a further limitation ofbeing only slightly light sensitive. For this reason, selenium has beenthe most commercially accepted material for use in electrophotographicplates. Vitreous selenium, however, while desirable in most aspects,suffers from serious limitations in that its spectral response issomewhat limited to the ultraviolet, blue and green region of thespectrum, and the preparation of vitreous selenium plates requirescostly and complex procedures, such as vacuum evaporation. Also.selenium plates require the use ofa separate conductive substrate layer,preferably with an additional barrier layer deposited thereon beforedeposition of the selenium photoconductor. Because of these economic andcommercial considerations, there have been many recent efforts towardsdeveloping photoconductive insulating materials other than selenium foruse in electrophotographic plates.

It has been proposed that various two-component materials be used inphotconductive insulating layers used in electrophotographic plates. Forexample, the use of inorganic photoconductive pigment dispersed insuitable binder materials to form photoconductive insulating layers isknown. It has further been demonstralcd that organic photoconductiveinsulating dyes and wide variety of polycyclic compounds may be usedtogether with suitable resinmaterials to form photoconductive insulatinglayers useful in binder-type plates. in each of these two systems, it isnecessary that at least one original component used to prepare thephotoconductive insulating layer be, itself, a photoconductiveinsulating material.

In a third type plate, inherently photoconductive polymers are used;frequently in combination with sensitizing dyes or Lewis acids to formphotoconductive insulating layers. Again, in these plates at least onephotoconductive insulating component is necessary in the formation ofthe layer. While the concept of sensitizing photoconductors is itselfcommercially useful, it does have the drawback of being limited to onlythose materials already having substantial photoconductivity.

The above discussed three types of known plates are further described inU.S. Pat. Nos. 2,999,750; 3,037,861; 3,041,165; 3,072,479; 3,097,095;3,113,022; 3,126,281; 3,159,483; 3,237,119;

3,484,237; 3,607,258; Canadian Pat. No. 644,167 and German Pat. No.1,068,115.

The polymeric and binder-type organic photoconductor plates of the priorart generally have the inherent disadvantages of high cost ofmanufacture, brittleness, and poor adhesion to supporting substrates. Anumber of these photoconductive insulating layers have low temperaturedistortion properties which make them undesirable in an automaticelectrophotographic apparatus which often includes powerful lamps andthermal fusing devices which tend to heat the xerographic plate. Also,the choice of physical properties has been limited by the necessity ofusing only inherently photoconductive materials.

inorganic pigment-binder plates are limited in usefulness because theyare often opaque and are thus limited to use in systems where lighttransmission is not re' quired. Inorganic pigment-binder plates have thefur ther disadvantage of being non-reusable due to high fatigue andrough surfaces which make cleaning difficult. Still another disadvantageis that the materials used have been limited to those having inherentphotoconductive insulating properties.

SUMMARY OF THE INVENTION it is an object of the invention to provide acomposition which is photoconductive and can readily be processed so asto form a photoconductive structure.

It is another object of this invention to provide a photoconductiveinsulating material devoid of the above noted disadvantages.

It has now been found that the problems of the prior art can be overcomethrough the use of a Lewis acid, preferably trinitro-fluorenone incombination with N- aryl carbazole characterized by the followingformula:

wherein X and Y are each selected from the group consisting of H, Cl, Brand NO and wherein Ar is selected from the group consisting of phenyl,napthyl and phenanthryl. The phenyl is advantageously a substitutedphenyl having the following structural formula:

wherein:

R and R are selected from the group consisting of H, N and COOH; R isselected from the group consisting of H, N(CH C.,H N0 oNO CH H.,-NH,o-NH -C,,H,NH. and Br.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The photoconductive materialadaptable for use in electrophotographic processes includes an electrondonor and an electron acceptor in the form of a charge transfer complexWhile the mechanism ofthe complex chemical interreaction involved in thepresent process is not completely understood, it is believed that acharge transfer complex" is formed having absorption bandscharacteristic of neither of the two components considered individually.The mixture of the two non or poorly photoconductive components seems tohave a synergistic effect which is much greater than additive.

The electron acceptor may be any suitable Lewis acid and the preferredgroup of Lewis acids are 2, 4, 7-trinitro-9-fluorenone; 2. 4, 5,7-tetranitro-9- fluorenone; 2, 6-dichloro-p-benzoquinone; 2, S-dinitro-9-lluorenone; l.5-dichloro-2, 4-dinitrobenzene; 2, -dichloropbenzoquinone; 2, 3. o-trichloro-pbenzoquinone; 2-chloro-3.S-dinitropyridine; 2,4,5, 7, Q-pentanitroindeue; 2, l-alpha 7lluorene-ll, 12- dione; 2. 5-diphenyl-pbenzoquinone; 2, 3-dichloro-l,4-naphthoquinonc1 9-dicyanomethylene-2, 4, 7- trinitrofluorene. Of thesethe most preferred are 2, 4, 7-trinitro9-fluorenone and 2. 4, 5,7-tetrariitro-9- fluorenone, These two electron acceptors givesubstantially increased electrophotographic speed over those listedabove or with respect to Lewis acids in general.

Other typical Lewis acids are: quinones, such as P- benzoquinone,chloranil, naphthoquinone-(l,4), 2,3- dichloronaphthoquinone-(1,4),anthraquinone, 2- methylanthraquinone, l,4-dimethylanthraquinone,chloroanthraquinone, anthraquinone-2-carboxylic acid,l,S-dichloroanthraquinone, l-chloro4- nitroanthraquinone,phenanthrenequinone, acenapthenequinone. pyranthrenequinone,chrysenequinone, thio-naphthenequinone. anthraquinone!,S-disulfonic acidand anthraquinone-Z-aldehyde; triphthaloylbenzene-aldehydes such asbromal, 4-nitrobenzaldehyde,

2.6-dichlorobenzaldehyde-9, 2-eth0xyl naphthaldehyde,anthracene-J-aldehyde, pyrene-3- aldehyde. oxindole-3-aldehyde,pyridine-2,6-

dialdehyde. biphenyl-4-aldehyde; organic phosphonic acid such as4-chloro-3-nitrobenzene-phosphonic acid, nitrophenols, such as4-nitrophenol, and picric acid; acid anhydrides. for example,acetic-anhydride. succinic anhydride. maleic anhydride. phthalicanhydride, letrachlorophthalic anhydride, perylene-3,4,9,]O-tetracarboxylic acid and chrysene-2,3,8,9- tetracarboxylic anhydride.di-bromo maleic acid anhydride. metal halides of the metals andmetalloids of the groups IE, I] through to group VIII of the periodicalsystem, for example: aluminum chloride. zinc chloride. ferric chloride,tin tetrachloride, (stannic chloride), arsenic trichloride. stannouschloride. antimony pentachloride, magnesium chloride, magnesium bromide.calcium bromide, calcium iodide, strontium bromide. chromic bromide,manganous chloride, cobaltous chloride, cobaltic chloride. cupricbromide. ceric chloride. thorium chloride, arsenic tri-iodine; boronhalide compounds, for example: boron trifluoride, and boron trichloride;and ketones, such as acetophenone. benzophenone. 2-acetylnaphthalene,benzil, benzoin, 5- benzoyl acenaphthene, biacene-dione,9-acetylanthracene. 9-benzoyl-anthracene,4-(4-dimethylamino-cinnamyl)-l-acetylbenzene, acetoacetic acid anilide,indandione-(l,3), 1,3-diketo-hydrindene, acenaphthene quinonedichloride.anisil, 2,2-pyridil and furil.

Additional Lewis acids are mineral acids such as the hydrogen halides,sulphuric acid and phosphoric acid; organic carboxylic acids, such asacetic acid and' the substitution products thereof, monochloro-aceticacid. dichloroacetic acid. trichloro-acetic acid. phenylacetic acid, and6-methylcoumarinylacetic acid (40); maleic acid, cinnamic acid, benzoicacid, l-(4-diethyl-aminobenzoyl)-benzene-2-carboxylic acid. phthalicacid. and tetra-chlorophthalic acid,alpha-betadibromo-betaformyl-acrylic acid (mucobromic acid). dibromomaleic acid. Z-bromo-benzoic acid, gallic acid,3-nitro-2-hydroxyl-l-ben2oic acid, Z-nitro phenoxyacetic acid.2-nitrobenzoic acid, 4-nitro-benzoic acid. 3-nitro-4-ethoxy-benzoicacid, 2-chloro-4-nitro-lbenzoic acid. 3-nitro-4-methoxy-ben2oic acid.4nitro-l-methyl-benzoic acid. 2-chloro5nitro-lbenzoic acid.3-chloro-6-nitro-l-benzoic acid. 4-chloro-3-nitro-l-benzoic acid,5-chloro-3-nitro-2- hydroxybenzoic acid, 4-chloro-2-hydroxy-benzoicacid. 2,4-dinitro-l-benzoic acid. Z-bromo-S-nitrobenzoic acid,4-chlorophenyl-acetic acid, 2-chlorocinnamic acid, Z-cyanocinnamic acid,2,4- dichlorobenzoic acid, 3,5-dinitro-benzoic acid,3,5-dinitro-salicylic acid, malonic acid, mucic acid,

acetosalicylic acid, benzilic acid, butane-tetracarboxylic acid, citricacid, cyano-aceitc acid, cyclo-hexane-dicarboxylic acid,cyclohexanecarboxylic acid, 9,]0-dichloro-stearic acid, fumaric acid.itaconic acid. levulinic acid (levulic acid), malic acid, succinic acid,alpha-bromo-stearic acid. citraconic acid, dibromo-succinic acid,pyrene-2.3,7,8- tetra-carboxylic acid, tartaric acid; organic sulphonicacids, such as 4-toluene sulphonic acid, and benzene sulphonic acid,2,4-dinitro-lmethyl-benzene-6- sulphonic acid,2,6-dinitro-l-hydroxy-benzene-4- sulphonic acid,Z-nitro-l-hydroxybenzene-4'sulphonic acid, 4-nitro-hydroxy-Z-benzenesulphonic acid, 3- nitro-2-methyl-l-hydroxy-benzene-S-sulphonic acid,6-nitro-4-methyl-l-hydroxy-benzene-Z-sulphonic acid, 4-chlorol-hydroxy-benzene-.'l-sulphonic acid, 2-chloro-3-nitro-l-methylbenzene-5-sulphonic acid and2-chloro-l-methyl-benzene-4-sulphonic acid.

The electron donor is an N-aryl carbazole characterized by the followingformula:

r wherein X and Y are selected from the group consisting of H, Cl, Brand NO, and wherein Ar is selected from the group consisting of phenyl,napthyl and phenanthryl. The phenyl is advantageously a substitutedphenyl having the following structural formula:

wherein:

R. and R are selected from the group consisting of H. NO and COOH;

R is selected from the group consisting of H. 3)2 CfiHfi, N020NO2C6H4NH, oNH -C H NH, and Br.

The following table sets forth advantageous combinations for R R and RAdvantageously, the photoconductor complex incudes a crystallizationprevention agent. The agent is a carbazolyl compound preferably adicarbazolyl cycloalkane such as dicarbazolyl cyclobutane.

EXAMPLE I A standard trinitrofluorenone/N-phenyl carbazole solution wasprepared by dissolving 2 grams (8.17 X mole) of N-phenyl carbazole in 3milliliters (ml.) of tetrahydrofuran and mixing the solution with asolution of 2.6 grams (8.25 X lO'" mole) of trinitrofluorenone dissolvedin l) ml. of tetrahydrofuran.

The solution is then coated on an aliminized Mylar substrate by adoctor-blade technique to a thickness of 0.2 mil. The coatingscrystallize almost immediately upon curing. However. even thoughcrystallized the coating had a charge acceptance of 300 volts and I2seconds of exposure to a 10 foot candle light source were required toreduce this voltage by half (l /2 120 foot candle sec).

EXAMPLE ll The conditions of Example I were repeated except that 0.3 gm(0.77 X l0 mole) of dicarbazolyl cyclobutane lopercent by weight) wasadded to the standard solution.

A 0.3 mil coating was produced. The coating did not crystallize uponcuring, and had a charge acceptance of 900 volts with a IV: 3.2 footcandle sec. The dicarbazolyl oyclobutane thus acted as a crystallizationprevention agent.

EXAMPLE Ill The conditions of Example I were followed except that theformulation comprised 22 ml. of tetrahydrofuran, 2.6 gm. oftrinitrofluorenone, 2 gm. of N-phenyl carbazole and 1 gram of MonsantoRP I323 as a binder. The charge acceptance was 520 volts and the 1 /2was 5.4 foot candle sec (fcs.).

EXAMPLE IV The conditions of Example III was followed except that 2 gmof the binder was used. The charge acceptance was I000 volts and the IV:was 12 f.c.s.

EXAMPLE V The standard solution of Example I was added l0 grams of asolution of 10 grams of poly N-vinyl carbazole (sold under the trademarkLuvican by BASF Co.) in ml. of tetrahydrofuran.

The solution was then coated on an aluminized Mylar substrate, by adoctor-blade technique, producing a 0.4 mil coating. The sample wastested in a Victoreen apparatus and was found to have a chargeacceptance of 1200 volts and required l.5 seconds to reduce thepotential to one half of its original value using a 1 foot candle light(1V2 i5 fcs). A 0.4 mil coating tested in a commerical xerographicphotocopier, gave L500 copies of good quality.

EXAMPLE VI A standard solution was prepared as described in Example l.Three ml. of a solution of 10 grams of polystyrene (sold under thetrademark PS 3, by Dow Chemical Co.) in 30 ml. of tetrahydrofuran wasmixed with the standard solution and a 0.2 mil coating was applied to analuminized Mylar substrate.

The charge acceptance was found to be 450 volts. and the 1% 3.2 fcs.

EXAMPLE VII The procedure of Example V was followed except that l gramof solution polyester 49000 (sold by Du Pont) was mixed with thestandard solution.

A 0.3 mil coating was found to have a t /z 50 fcs. and a chargeacceptance of 500 volts.

What is claimed is:

l. A photoconductive electrically insulating composition comprising acharge transfer complex of a Lewis acid and an N-aryl carbazole,characterized by the structural formula:

wherein X and Y are each selected from the group consisting of N, Cl,Br. and NO; wherein Ar is selected from the group consisting of phenyl.naphthyl and phenanthryl; wherein said Lewis acid is taken from thegroup consisting of 2,4,7-trinitro-9-fluorenone; 2.4.5.7-tetranitro-9-fluorenone; 2,b-dichloro-p-benzoquinone;2,5-dinitro-9-fluorenone', l,5-dichloro-2,4' dinitrobenzene;2,5-dichloro-p-benzoquinone; 2.3,6-

3. A photoconductive electrically insulating composition comprising acharge transfer complex of an electron acceptor taken from the groupconsisting of 2,4,7-trinitro-9-fluoreneone and 2, 4. 5, 7-tetranitro-9-fluoreno ne and an electron donor as N-phenyl carbazole, the ratioofelectron acceptor to donor being from 5:! to l:l and includingdicarbazolyl cyclobutane in an amount sufficient to preventcrystallization of said composition.

1. A PHOTOCONDUCTIVE ELECTRICALLY INSULATING COMPOSITION COMPRISING AHCARGE TRANSFER COMPLEX OF A LEWIS ACID AND AN N-ARYL CARBAZOLE,CHARACTERIZED BY THE STRUCTURAL FORMULA:
 2. The composition defined inclaim 1 wherein said dicarbazolyl cycloalkane is dicarbazolylcyclobutane.
 3. A photoconductive electrically insulating compositioncomprising a charge transfer complex of an electron acceptor taken fromthe group consisting of 2,4,7-trinitro-9-fluoreneone and 2, 4, 5,7-tetranitro-9-fluorenone and an electron donor as N-phenyl carbazole,the ratio of electron acceptor to donor being from 5:1 to 1:1 andincluding dicarbazolyl cyclobutane in an amount sufficient to preventcrystallization of said composition.